Fix bugs and make improvements

- Get clone() working on FreeBSD
- Increase some Python build quotas
- Add more atomic builtins to chibicc
- Fix ASAN poisoning of alloca() memory
- Make MODE= mandatory link path tinier
- Improve the examples folder a little bit
- Start working on some more resource limits
- Make the linenoise auto-complete UI as good as GNU readline
- Update compile.com, avoiding AVX codegen on non-AVX systems
- Make sure empty path to syscalls like opendir raises ENOENT
- Correctly polyfill ENOENT vs. ENOTDIR on the New Technology
- Port bestline's paredit features to //third_party/linenoise
- Remove workarounds for RHEL 5.0 bugs that were fixed in 5.1

libc/log/oncrash.c

@@ -64,8 +64,6 @@ relegated static void ShowFunctionCalls(ucontext_t *ctx) {
   struct StackFrame goodframe;
   if (!ctx->uc_mcontext.rip) {
     kprintf("%s is NULL can't show backtrace%n", "RIP");
-  } else if (!ctx->uc_mcontext.rbp) {
-    kprintf("%s is NULL can't show backtrace%n", "RBP");
   } else {
     goodframe.next = (struct StackFrame *)ctx->uc_mcontext.rbp;
     goodframe.addr = ctx->uc_mcontext.rip;
@@ -142,7 +140,7 @@ relegated static void ShowGeneralRegisters(ucontext_t *ctx) {
     }
   }
   DescribeCpuFlags(
-      p, ctx->uc_mcontext.gregs[REG_EFL],
+      p, ctx->uc_mcontext.eflags,
       ctx->uc_mcontext.fpregs ? ctx->uc_mcontext.fpregs->swd : 0,
       ctx->uc_mcontext.fpregs ? ctx->uc_mcontext.fpregs->mxcsr : 0);
   kprintf("%s%n", buf);